The exhaust air handling unit  works as a supplier of fresh air into the building. The exhaust air is discharged for securing an indoor air quality which is acceptable. Depending on the required temperature of the air,  fresh air is heated by the recovery unit or the heating coil. It is also cooled by the cooling coil. In many buildings, where the requirements for air quality is lower, some of the air from the rooms has to be re-circulated by the mixing chamber resulting in significant energy savings. The mixing chamber used here has the dampers for controlling the ratio between the return, outside, and exhaust air.